Various systems and methods of lifting and moving heavy objects have been developed. Some systems such as a gantry crane system use pairs of lift towers to lift a heavy object. Each lift tower includes a single hydraulic cylinder on a base which extend and retract to raise and lower the object. The lift cylinders may be single or multi-stage. In some cases, the lift towers may include a frame or boom member surrounding the hydraulic cylinders.
Safety devices are typically used with the lift towers to prevent or reduce the likelihood that a heavy object will be inadvertently lowered. Some systems use mechanical pins or rods that extend into holes in the boom to mechanically secure the lift towers at certain predetermined positions. Other systems such as that disclosed in U.S. Pat. No. 8,322,687 A1 utilize a wedge lock system to provide a mechanical lock to prevent inadvertent retraction of the lift towers.
In addition, the valves within the hydraulic system may be configured to also reduce the likelihood of inadvertently lowering of a heavy object. For example, the valves used to direct the flow of hydraulic fluid may limit the flow of hydraulic fluid from the hydraulic cylinders and thus, to some extent, maintain the hydraulic cylinders in position even in the absence of hydraulic pressure from the source. Still further, counterbalance or check valves may be used to permit the flow of hydraulic fluid in one direction but prevent flow in an opposite direction absent a desired level of hydraulic pressure controlling the counterbalance valve.
In the event of a failure within the hydraulic system, the lift towers will be retained in their extended condition supporting the load of the lifted object. This condition presents an especially undesirable environment for repair of the hydraulic system and contributes to an overall delay in reaching the objective associated with the purpose of the lift. Accordingly, it has been determined that a system for redundant operation of the lift towers is a desirable attribute of a system and an enhancement of overall safety. It has been determined that a desirable feature of such hydraulic lift systems would be to provide alternative lift capability in the event of incapacity of the main lift cylinders.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein, nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.